A conventional cylinder type engine produces power by converting thermodynamic energy from gas combustion in cylindrical chambers into reciprocating rectilinear kinetic energy. The reciprocating rectilinear motion is converted into a complete rotary motion through a crank unit. In this process, a mechanical power loss arises due to the frictions and vibrations caused by the changes in motion directions.
As a method to overcome the aforementioned problems, rotary engines capable of generating unidirectional motion are utilized. The only rotary engine currently adopted in a production model is the Wankel engine, in which a triangular rotor moves along epitrochoid in housing. In the Wankel engine, each vertex of a triangle plays the role of gas seal in the process of intake, compression, combustion and exhaustion. However, in this case, the increased friction and problematic lubrication between the rotor vertices and cylinder wall may cause rotor vertex abrasion, and consequently the gas sealing function may deteriorate.
Also, due to the abrasion of rotor vertices, the engine itself needs to be redisposed with new one periodically. In order to solve the problems in conventional cylinder type engines, many attempts other than the Wankel engine were made, especially in the form of rotary engine with reciprocating motion.
However, in order to commercialize these rotary type engines, there remain many difficult problems such as designing the structure of combustion chamber and intake/exhaust devices suitable for practical uses in high performance engines and converting the reciprocating rotary motion into a complete rotary motion.
On the other hand, in order to convert the eccentric torque of the Wankel engine or the reciprocating torque of other rotary engines into a complete concentric torque, the direction of force must be changed mechanically. However, a power conversion using only mechanical methods inevitably accompanies frictions and vibrations due to the changes of power directions in power train. Accordingly, a power conversion system utilizing electric motors, which are more reliable in terms of control certainty and effectiveness, may be suggested as a substitute to improve the effectiveness in comparison with existing concepts.
Also, when considering the environmental problems and energy efficiency, the development of an internal combustion-electric hybrid engine is being recognized as an essential task in automobile industry. Currently, several types of hybrid vehicles are in commercial production in Japan, the U.S.A., etc, and they are proven to improve the fuel efficiency. The general principle of a hybrid system is rather simple. Namely, the hybrid system is to increase the fuel efficiency by effectively operating the power from an internal-combustion engine and the power from an electric motor according to the driving conditions. A hybrid car named Prius by Toyota Company is recognized as one of the most successful model among currently commercialized hybrid automobiles, and it uses a system called “power splitter” for interconnection of powers from a cylindrical type engine, an electric motor and a generator, reciprocally converting mechanical energy and electric energy, to thereby utilize the power most effectively.
Although there are some differences between production models, other systems are also based on similar principles. Hybrid systems utilizing a cylinder type engine and an electric motor may differ from each other according to methods of connecting the power generating devices, but they must include an electric motor and a storage battery in addition to an internal-combustion engine. Accordingly, the weight of power train inevitably increases. Methods for solving the aforementioned problems by improving the electric motor design and battery performance, and etc are being studied, but eventually the most effective method is to reduce the weight of the internal-combustion engine, which is the heaviest component. Other than some experimental models, most hybrid cars in production utilize the existing cylinder type engine. Accordingly, the fundamental solutions to the aforementioned problems are not found yet.